The present invention relates to a method and apparatus for deflashing molded recorded discs, and particularly to a method and apparatus for cutting the edge of the molded disc to a controlled size after removing the major portion of the flash by a knife.
Recorded discs are flat, circular plates of a plastic material having information on one or both surfaces thereof in the form of a surface relief pattern formed along a spiral path. Generally, the surface relief pattern is formed in a spiral groove in the surface of the disc. The discs are generally formed in a mold press having a pair of mold plates, at least one of which is movable toward and away from the other and which, when together, form a mold cavity therebetween of the size and shape of the disc. On the opposed surfaces of the plates are stampers which have on their surfaces the negative of the surface relief pattern to be formed in the surfaces of the disc. When a disc is molded in such a mold press, excess plastic material flows radially outwardly beyond the edge of the mold cavity so that the molded disc has excess material around its edge, known as "flash", which must be removed. This removal of the flash is generally achieved by placing the still warm disc directly from the mold press onto a circular support plate with the flash projecting beyond the edge of the plate and rotating the plate. A knife is pressed against the rotating disc so that the knife cuts off the flash up to the edge of the disc. Such an apparatus is shown in U.S. Pat. No. 3,412,427 to J. Flushfeder et al, issued Nov. 26, 1968, entitled "Apparatus For Manufacturing Disc Records".
Recently there has been developed a high density recorded disc, such as a video disc, which contains a large number of revolutions of the recorded path, about 10,000 per inch along the radius of the disc. One type of such recorded disc is made of a plastic material which is filled with conductive carbon so that the disc is conductive. This type of disc is more brittle than discs which do not contain the conductive carbon. It has been found that when the flash is removed from this type of disc by means of a knife, the edge of the disc is not smooth. Also, since the disc is more difficult to cut with a knife, it is difficult to accurately control the diameter of the disc after flash removal. It has been found desirable to place this type of disc in a carrier or caddy to protect the surface of the disc from dirt and other contaminants. In order to permit the disc to be removed from and replaced into the caddy, it is desirable to accurately control the diameter dimension of the disc. Therefore, it is desirable to have means for removing the flash from the disc which provides the disc with a smooth edge and which will permit accurate control of the diameter of the disc.